Please use a symbols file for linking

Using a symbols file that hides internal symbols for linking in the library would be great to avoid 'grey areas' like #174 (closed). One way to do this would be s.th. like:

LIBMMGLIB_0 {
	global:
		mm_*;
	local:
		*;
};

(and then do s.th. like https://source.puri.sm/Librem5/libhandy/blob/master/src/meson.build#L185)

and prefixing internal symbols with _mm_ (so they don't match mm_). Alternatively either global or local symbols could be listed explicitly. This also allows for marking newer symbols as such like e.g. libvirt does:

https://libvirt.org/git/?p=libvirt.git;a=blob;f=src/libvirt_lxc.syms

(the symbols file is split across several files there).